Organic antioxidant dynamics in Hydrangea macrophylla Ser. leaves in humid subtropics of Russia

Abstract

Subtropical ornamental crops have been cultivated and studied in the humid subtropics of Russia for over a century. Nevertheless, a comprehensive evidence on their adaptation and stress is rather scarce for the region. The climatic conditions in Russian humid subtropics may occur extreme to introduced plants, which warrants research into their adaptive reactions to soil aridity and summer temperatures over +30 C°. Given the situation, understanding the mechanisms of main stressor-adaptive responses is relevant in ornamental crops, including Hydrangea macrophylla Ser. Gas chromatography-mass spectrometry  was  employed  to study ethanol leaf extracts in various-hardiness Hydrangea macrophylla Ser. cultivars, relatively hardy (Draps Wonder, Admiration, Altona), medium-hardy  (Souer Theresa) and susceptible (Harlequin, Madame Faustin) forms. Eleven endogenous organic compounds have been identified, of most interest being antioxidants and stress-protectants, including diarylethylene aromatic hydrocarbons (2,4’-dihydroxystilbene), squalene and phytosterines (y/p-sitosterol). The organic leaf content changed in response to hydrothermal stress in H. macrophylla, with a maximal concentration (2,4’-dihydroxystilbene 14.0, sitosterol 5.7 %) observed in favourable hydrothermal conditions of April, and minimal —  in the first August decade (8.5 and 1.7 %, respectively). Meanwhile, the relatively hardy Draps Wonder, Admiration and Altona varieties possessed the highest organic content of 2,4’-dihydroxystilbene (18.4,  21.5,  21.6 %) and y/p-sitosterol (5.7,  7.5,  6.0 %) both in optimal and stressing times. The lowest synthesis in the periods was observed in the unstable H. macrophylla varieties, Madame Faustin (6.9 and  1.1 %) and Harlequin (7.6 and  1.4 %).